1. Field of the Invention
The present invention relates to a smoke detector for optically detecting contaminants such as smoke floating in the air, and a sampling air supplying method therefor.
2. Description of the Related Art
A smoke detector is used for preventing fire or as a detecting system at a time of occurrence of fire or in a semiconductor manufacturing plant or a food industry requiring a certain level of environmental conservation.
As the smoke detector, there is used a high-sensitive smoke detecting apparatus. In the high-sensitive smoke detecting apparatus, air is sucked from a warning area through a sampling pipe by driving a fan, light receiving signals are converted into pulse signals through a comparison between the light receiving signals and a threshold value using a comparator, the light receiving signals being obtained by irradiation of light whose beam spots are focused on smoke particles contained in the sucked air, and the number of the pulse signals are counted, thereby measuring a smoke amount (see Japanese Patent No. 3312712).
In a conventional example, a primary side (suction port side of fan) at which a fluid (sampling air) has not been applied with energy by a fan and a secondary side (exhaust port side) at which the fluid has been applied with energy are connected through a smoke detection portion of a black box, and by using a pressure difference between the primary side and the secondary side, the sampling air is supplied to the smoke detection portion.
Accordingly, depending on a state of a filter for filtration, which is provided to the fan or a pipe line, a sampling flow rate changes in some cases. When the sampling flow rate changes, due to P-Q characteristics of the fan, fluctuation is caused in the pressure difference between the primary side and the secondary side, and the sampling air cannot be supplied to the smoke detection portion at a preset flow velocity. Therefore, accurate smoke detection becomes difficult.